Padded envelope

ABSTRACT

The envelope comprises layers of plain un-coated kraft paper and of bubble-wrap polyethylene. A stack of the layers is joined at the marginal edges of the envelope by squeezing the stack between a pair of points-dies, which are formed with points that puncture the kraft paper but do not puncture the polyethylene. The points push crowns of un-punctured polyethylene through the punctured holes in the paper. Then, the marginal edges are squeezed flat between flat-dies, the flat-dies being heated enough to cause fuse-bonding. The margins of the finished envelope are held together not only by fuse-bonding, but by the presence of the crowns, which, penetrating right through the holes in the paper, serve as mechanical rivets.

[0001] This invention relates to padded envelopes, being envelopes thathave an outer covering of paper, and an inner lining of plastic bubblematerial. Plastic bubble-wrap is a well-known, widely-used, packagingmaterial, and comprises a flat-layer of a thin plastic, such aspolyethylene (polythene), and a bubble-layer of thin plastic, which ispartially laminated to, and partially separated from, the flat-layer.The areas of separation of the layers are isolated from each other,being completely surrounded by the laminated areas, to form the bubbles.

BACKGROUND TO THE INVENTION

[0002] In bubble envelopes, the flat-layer of the bubble material formsthe inside lining of the envelope, and is contacted directly by itemsplaced in the envelope, and the paper (usually, kraft paper) forms theoutside of the envelope.

[0003] With the traditional bubble padded envelopes, a problem can ariseregarding recycling of the envelopes, and regarding the re-use of thematerials from which the envelopes are made. The problem has been that,if the bubble material was adhered to the paper strongly enough toprovide a serviceably-robust structure, it was not possible tophysically separate the bubble material from the paper, so that thedifferent materials could be recycled.

[0004] Proposals have been made to attach the bubble material to thepaper in such a way as to permit separation for re-cycling, but theseproposals have been very expensive, or not mechanically satisfactory, orhave involved the use of applied adhesives, which require the use ofsophisticated handling and positioning machinery.

[0005] The invention is aimed at providing a bubble padded envelope, inwhich the bubble material is attached to the paper in a manner that issatisfactory from the service or usage standpoint, and which permits thebubble material to be readily separated from the paper, for recycling.

[0006] It is also an aim of the invention to provide a manner of makinga padded envelope, which provides a serviceably robust envelopestructure, by a simple manufacturing procedure that requires a minimumof costly preparation of the envelope components.

THE INVENTION IN RELATION TO THE PRIOR ART

[0007] An example of a prior design of bubble-padded envelope is shownin patent publication U.S. Pat. No. 6,139,188 (Marzano, 2000)

[0008] In one traditional design of bubble envelope, the paper and thebubble material were first attached face to face over the whole area ofthe bubble material. In order to enable the polyethylene bubbles tostick to the paper, the paper had to be itself coated with a thin layerof polyethylene, over its whole surface. Then, as a preliminaryproduction step in the manufacture of the envelopes, the bubble materialwas placed against the coated side of the paper, bubble-tips touchingthe paper, under conditions of heat and (slight) pressure, whereby thetips of the bubble became attached to the paper. In this traditionalmanufacturing system, only when the paper had been coated, and thebubble material then stuck face-to-face over the coated paper, couldmanufacture of the envelopes be commenced.

[0009] Envelopes manufactured by this traditional system, however,though very robust and serviceable, could not be recycled because thepolyethylene cannot later be separated from the paper. Also, this systeminvolved impregnating a coating of polyethylene into the kraft paper,prior to making the envelopes, which generally was carried out in aseparate factory from the manufacture of the envelope, and that couldsometimes lead to inventory inefficiencies, etc.

[0010] It should be understood that, in the above-described traditionalsystem, the securement of the bubble material to the coated paper, toform a layered composite, occurs over the whole interface betweenbubbles and paper. That is to say, the tip of every bubble adheres tothe paper. It is not practical for the bubbles to be adhered to thepaper over only a narrow band. The system provides that the bubble tipsare secured very firmly to the pre-coated paper, but the disadvantage isthat the bubble material cannot later be removed from the paper forrecycling.

[0011] It may be noted that polyethylene cannot be reliably bonded toun-coated paper, simply by squeezing the polyethylene against the paperbetween heated dies. The polyethylene will bond a little, but not enoughto be suitable for the manufacture of envelopes. Rather, the paper firsthas to undergo the pre-coating process, which leaves a thin film ofpolyethylene on the paper, in which case the polyethylene bubbles adhereto the paper such that the two materials cannot later be separated.

[0012] It is also known, for example from DE-4,343,798, to provide anadditive to be included in the bubble material, which can be activatedto cause the bubbles to adhere to the paper. Thus, the bubble materialmay be attached to un-coated paper, and this can be done by activatingthe additive over pre-determined narrow bands. This allows the bubblematerial to be attached to the paper over only the outer margins thatmake up the envelope. The bubbles are not attached to the paper over themajority of the surfaces that comprise the envelope. This system canproduce satisfactory results, in that the envelopes are serviceable, yetthe envelopes can be torn apart, after use, and the paper and bubblematerial separated for recycling. However, the system is expensive, andprone to manufacturing difficulties.

[0013] The invention is also aimed at providing an envelope in which thebubble material is attached to the paper only at the edges or margins ofthe envelope. Thus, again, the bubble material may be separated from thepaper for recycling after use. But the invention provides a manner ofattaching the bubble material to the paper in such a manner that nopre-coating of the paper is needed, nor adhesives, nor other items thatcan lead to production difficulties.

[0014] The invention is aimed at providing a manner of attaching thebubble material to the paper in a manner that is predominantly amechanical interaction between the paper and the bubble material, ratherthan a chemical adhesive interaction. In the invention, the aim is toenable padded envelopes to be made using, as starting materials, a rollof inexpensive plain un-coated paper and a roll of plain bubblematerial, and to attach the two materials to form an envelopeconfiguration, by a simple clean production process. It is an aim of theinvention that no adhesives or additives be required.

GENERAL FEATURES OF THE INVENTION

[0015] In one aspect, the invention lies in a procedure, as claimed, forjoining a sheet of paper to a sheet of plastic bubble-wrap material.More particularly, the invention lies in a procedure, as claimed, formanufacturing a padded envelope. In another aspect, the invention liesin an envelope that has been manufactured by that procedure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] By way of further explanation of the invention, exemplaryembodiments of the invention will now be described with reference to theaccompanying drawings, in which:

[0017]FIG. 1 is a pictorial view of a padded envelope that embodies theinvention.

[0018]FIG. 1a is a sectioned side-elevation of the envelope of FIG. 1.

[0019]FIG. 2 is a diagram of production apparatus used for manufacturingthe envelope of FIG. 1.

[0020]FIG. 3 is a cross-sectioned end-elevation in the direction ofarrows 3-3 of FIG. 2.

[0021]FIG. 4 is a plan view of a stack of layers as it passes throughthe apparatus of FIG. 2.

[0022]FIG. 5 is an elevation showing a stack of layers and showing apair of points-dies of the apparatus of FIG. 2, prior to the points-diesbeing brought together onto the stack.

[0023]FIG. 6a is a pictorial view of one of the points-dies of theapparatus of FIG. 2.

[0024]FIG. 6b is a pictorial view like that of FIG. 6a, but showing adiagonal arrangement of points.

[0025]FIG. 7 is a close-up showing a portion of the stack, as squeezedbetween the points-dies.

[0026]FIG. 8 is the same close-up as FIG. 7, but after the points-dieshave been withdrawn from the stack.

[0027]FIG. 9 is a close up of the same portion as FIGS. 7 and 8, butafter the stack has been squashed flat by flat-dies of the apparatus ofFIG. 2.

[0028]FIG. 10 is an elevation showing an alternative construction of thepoints-dies.

[0029]FIG. 11 is a corresponding elevation showing another alternativeconstruction of the points-dies.

[0030]FIG. 12a is a diagram illustrating a slack-take-up position of thedies.

[0031]FIG. 12b is a diagram illustrating a closed-together position ofthe dies.

[0032]FIG. 13 is a diagram illustrating a layout of points.

[0033] The apparatuses and procedures shown in the accompanying drawingsand described below are examples which embody the invention. It shouldbe noted that the scope of the invention is defined by the accompanyingclaims, and not necessarily by specific features of exemplaryembodiments.

[0034] The padded envelope 20 of FIGS. 1 and 1a comprises a top T and abottom B, which are secured along their marginal far edge 24, and alongtheir marginal left and right side edges 25L,25R, to create a pocket 26.The top T comprises an outer layer 27T of kraft paper 27, and an innerlayer 29T of polyethylene bubble-wrap material 29. The bottom Bsimilarly comprises an outer layer 27B of the kraft paper 27, and aninner layer 29B of the polyethylene bubble material 29.

[0035] Typically, the kraft paper is about a hundred microns thick, andthe polyethylene film from which the bubble-wrap material is made isabout fifty microns thick. Typically, the bubbles have a diameter ofeight mm, are spaced on a hexagonal grid with a ten mm centre-to-centredistance, and the bubbles stand four mm high.

[0036] At the mouth of the pocket 26, the bubble layer 29T is adhered tothe paper layer 27T, and the bubble layer 29B is adhered to the paperlayer 27B, whereby the mouth 30 of the pocket comprises an openingbetween the top bubble-layer 29T and the bottom bubble-layer 29B.

[0037] Some of the stages in the manufacture of the envelope areillustrated in FIG. 2. The manufacturing apparatus 31 includes a firststation 32 (see also FIG. 3), at which the left and right edges of thetop layer 27T of paper are hot-pressed onto the left and right edges ofthe top layer 29T of bubble, using heated dies 33LT,33RT, whereby thebubbles 35 are squashed flat, and the polyethylene adheres to the paper,to form bonded margins 34LT,34RT. Also, the left and right edges of thebottom layer 27B of paper are hot-pressed onto the bottom layer 29Bbubble, using heated dies 33LB,33RB, whereby the bubbles of the bottomlayer 29B are squashed flat, and the polyethylene adheres to the paper,to form bonded margins 34LB,34RB.

[0038] These margins 34LT,34RT,34LB,34RB will later form the lips of themouth 30 of the pocket 26. Again, it should be noted that the securitylevel of the kind of adherence that arises from simply hot-pressingpolyethylene onto un-coated paper is not very high, but in fact theadherence only needs to be adequate for the task of keeping the mouth ofthe pocket open, and hot-pressing onto un-coated paper is enough forthat.

[0039] The top layers 27T,29T are kept separate from the bottom layers27B,29B, while being processed in the first station 32. The two toplayers emerge from the first station joined at the marginal edges34LT,34RT but not joined over the rest of the area of the layers.Similarly, the two bottom layers move forward to the second station,joined just at the marginal edges 34LB,34RB. The two top layers 27T,29Tand the two bottom layers 27B,29B advance separately to the secondstation 36.

[0040] At the second station 36, the top layers 27T,29T of paper andbubble are joined to the bottom layers 27B,29B of paper and bubble, theareas of the joints being arranged in bands, which will later correspondto the marginal edges of the manufactured envelopes. FIG. 4 shows theconfiguration of the joint-bands 37 in plan view.

[0041]FIG. 5 is a view showing the stack 38 of layers, comprising toppaper 27T-top bubble 29T-bottom bubble 29B-bottom paper 27B. Also shownis a pair of dies 39T,39B. Both dies are formed with points 40. FIG. 6ais a pictorial view of one of the points-dies 39B.

[0042] When the points-dies are brought together, the stack 38 of layersis trapped therebetween. As the dies come together, the bubbles 35located between the dies are squashed flat. The portion of the stacktrapped between the points-dies is then forced to follow the contours ofthe points 40.

[0043] It is a characteristic of paper, including the kraft paper 27from which padded envelopes are made, that when a point is pressed intoa sheet of paper, the paper can stretch resiliently to only a verylimited extent. The paper will easily tear, i.e will be punctured, if asharp point is pressed into the paper. Paper can stretch resiliently toonly a limited extent. Paper does have a yield point, in that, ifslightly over-stressed, paper will take a permanent set, withouttearing. But it does not take much extra stress, beyond that, for paperto tear.

[0044] Polyethylene, including the polyethylene from which bubblematerial 29 is made, on the other hand, has a much larger capacity thanpaper, when over-stressed, to yield, and to carry on yielding, withoutpuncturing.

[0045] It is recognised that, when a point is pressed into the stack 38of layers of paper and polyethylene, the effect is that the paper layersbecome punctured; the polyethylene layers yield, and become stretched,but the polyethylene is not punctured. It is recognised that each point40, if configured properly, can be arranged to push a crown ofun-punctured polyethylene right through the hole the point has puncturedin the paper.

[0046] In the condition as illustrated in FIG. 7, the points 40 on thepoints-dies 39T,39B have punctured holes right through the top andbottom layers 27T,27B of paper. The points have stretched the top andbottom layers 29T,29B of polyethylene beyond yielding, but have notpunctured the polyethylene.

[0047]FIG. 8 illustrates the condition of the stack when the points-dies39T,39B are withdrawn. A small crown 42 of over-stretched polyethyleneprotrudes through the paper. If the FIG. 8 stack is held up to thelight, points of light should be seen through the stack, indicating thatthe paper has been punctured; but, to repeat, only the paper has beenpunctured, not the polyethylene.

[0048] The stack 38 is now transferred to the third station 43 (FIG. 2).In this station, the stack is pressed between two flat-dies 45T,45B.These dies simply squash the FIG. 8 stack flat. The crowns 42 arecompressed, from the outside of the paper, down onto the paper. Thus thecrowns serve as mechanical rivets, holding the paper firmly secured tothe polyethylene. Now, the condition of the squashed stack is asillustrated in FIG. 9.

[0049] The flat-dies 45T,45B are supplied with heat, and apply heat tothe polyethylene, to the extent that the polyethylene is heated beyondits thermoplastic limit. When it cools, the polyethylene acquires theFIG. 9 shape permanently. As a result, the stack of paper andpolyethylene layers is held together securely, by a combination offuse-bonding and mechanical interaction.

[0050] At the cutting station, or fourth station 46, the envelopes arefinished by cutting out, along the cut-lines 49 as indicated in FIG. 4.Also, strips 47 of press-to-stick adhesive are applied to the flaps 48.

[0051] The points 40 on the points-dies 39T,39B, as shown in FIG. 6a,comprise pyramids 50, which are relatively easy to manufacture, beingformed by grinding grooves in a solid slab of metal. The pyramids arepitched on a square grid, at around two or three millimetres apart. Thetips of the pyramids are sharp, as are the four side edges of thepyramids.

[0052] Alternatively, as shown in FIG. 10, the points-dies 52T,52B mayinclude needles. The needles 53 are manufactured separately from theslab 54 of the die, and pressed into sockets 56 therein. The needles 53again form a square grid, pitched at around two or three mm apart. Thetips 57 of the individual needles preferably are not sharp, but have aradius of ½ or ¼ mm. A very sharp point on the tip 57 might lead to theunwanted puncture of the polyethylene, whereas the radiused tip canstretch the polyethylene as much as ten mm before puncture. On the otherhand, the radiused tip is almost the equal of a sharp tip when it comesto puncturing the paper.

[0053] It may be noted that, in regard to the pyramids-style points-dies39T,39B of FIG. 6a, the pyramids of the top die 39T are an exact fit tothe pyramids of the bottom die 39B. Thus, when the points-dies 39T,39Bare brought together, the whole surface area of the stack 38 is squeezedand compressed between the dies. That is to say, as the points 40 of thepyramids penetrate the paper, and drive the crowns 42 of polyethylenethrough the holes in the paper, the rest of the stack of layers aroundthe points is squashed flat.

[0054] As shown in FIG. 6b, the points may alternatively be arranged indiagonal rows.

[0055] But it is not essential that the area of the stack around thepoints be squashed flat by the points-dies, as happens with thepyramids-style of points-die, since the flat-dies 45T,45B will squeezethe stack flat. The needles-style of points-die 52T,52B leaves the areaof the materials immediately surrounding the points un-compressed, whichcan be an advantage in that the polyethylene can then the more easilyflow into the crowns without being over-stretched. Variousconfigurations are contemplated, of sharp points or rounded points, of aone-piece die or needles let into sockets, of relief around the pointsor the dies closing together over the whole are, and the like. The costof making the dies is one factor, and the quality of the finishedenvelopes is another.

[0056] The use of the needles-style of points-die 52T,52B may beexpected to create larger crowns, i.e larger buttons of polyethylenethat have been punched right through the paper to the other side of thepaper, than the pyramids-style of points-die 39T,39B. Again, in FIG. 10,the stack of layers is squeezed flat between heated flat-dies 45T,45B,after the stack has been separated from the points-dies.

[0057] It is essential that the points puncture right through the paper,but it is not essential that half the points penetrate through from oneside, and half from the other side, in the symmetrically alternatingup/down manner as illustrated in FIG. 7. All the punctures may be fromone side, if the designer wishes to arrange the dies that way. Aneedles-type points-die, in which the needles press only from one side,is shown in FIG. 11.

[0058] The punctures through the paper must be in the form of smallpoints, each of which is surrounded by un-ruptured paper. It would notbe acceptable for the paper to be punctured along a continuous line, forinstance, because that would mechanically weaken the material.Similarly, the punctured points should not, in the finished envelope,form a line of perforations, whereby the envelope might easily be tornalong that line.

[0059] If just one, or a few, of the points were to puncture, i.e make ahole right through, the polyethylene, that would not matter in itself;however, generally, for the security of the envelope, the polyethyleneshould not be punctured, and the presence of even one puncture mightindicate that an inadequate margin of tolerance had been provided.

[0060] The dies 45T,45B;39T,39B;52T,52B as depicted herein have been inthe form of flat slabs. In use, the stack 38 of layers is advancedthrough and between the dies, and then the movement of the stack ishalted, and the dies are brought together and pressed onto thenow-stationary stack. After the dies are separated, the stack is thenadvanced to the next station. The cycle time for drawing the stackforward is dictated by the length of time it takes to ensure that thepolyethylene reaches its thermoplastic temperature, in the flat-diesstation (i.e the third station 43).

[0061] The points-dies 39T,39B;52T,52B may be heated (in the secondstation 36). This enables the overall cycle-time to be reduced, in thatthe time the stack must spend between the flat-dies 45T,45B (in thethird station 43) can be reduced, since the materials in the stack arepre-heated before reaching the third station.

[0062] Rather than being in the form of flat slabs, the dies may be inthe form of rollers. In that case, the stack may be passed through therollers without the cyclic stopping that is required when the dies areflat slabs. It may be noted that the term “flat” in the flat-dies refersto the effect of the dies in squashing the stack flat, not in the shapeof the dies. Thus, the flat-dies may actually be rollers.

[0063] Similarly, the flat-dies may have the effect of impressing thewhole area of the margin with, for example, an overallrounded-corrugated form (e.g corrugated in the view of FIG. 9), andstill have the effect of squashing the crowns flat onto the outsidesurfaces of the paper, as required in the invention.

[0064] As shown, the far end 24 of the envelope 20 is made in the samemanner as the side-edges 25L,25R, i.e by squeeze-bonding the joint-bands37. The joint-bands 37 should be about two cm wide, whereby the bondedmargin at the edges 24,25L,25R of the finished envelope each have awidth of about one cm, when the envelopes are cut or stamped out, at thefourth station 46, along the cut-lines 49.

[0065] Alternatively, the designer may prefer to form the far edge 24,not by squeeze-bonding, but simply by folding the layers over, wherebythe top and bottom layers 27T,27B of paper are formed from a singlefolded-over sheet of paper, and the top and bottom layers 29T,29B ofpolyethylene are formed from a single folded-over sheet of polyethylene,and the squeeze-bonding occurs just at the left and right edges 25L,25R.This manner of forming the end of an envelope is depicted in the saidU.S. Pat. No. 6,139,188, for example. Of course, folding the edge 24requires sophisticated fold-making machinery.

[0066] As mentioned, the preferred application of the materials jointingsystem described herein is in making padded envelopes from polyethylenebubble-wrap and kraft paper. However, padded envelopes can be made fromother materials. For example, the polyethylene bubble-wrap may bereplaced with expanded polyethylene foam. Being polyethylene, suchexpanded foam material again is thermoplastic, and has a greatresistance to being punctured.

[0067] Many other plastic materials have the capacity to be heatedbeyond a thermoplastic limit and to regain mechanical properties uponcooling, and have also the ability to become stretched rather than topuncture, when stressed by a sharp point, such a polypropylene, nylon,etc. These materials may be considered for use in the invention, inwhich the main requirement is that un-punctured crowns of thethermoplastic film material can be pressed through punctured holes inthe other material, and the crowns can then be heat-bonded to thepunctured material.

[0068] Also, in the broad scope of the invention, the thermoplasticmaterial need not be in bubble form, or expanded form, but may be in theform of just a single sheet or film.

[0069] The puncture-able material may be other than paper. The maincharacteristic required in this other material is that it be capable ofbeing punctured when pressed by a sharp point. The material may be afabric or cloth, for example; or the material may be a metal foil, forexample aluminum foil. Some speciality envelopes are made now usingcloth or aluminum foil.

[0070] As described above, a bubble envelope comprised layers of plainun-coated kraft paper and of bubble-wrap polyethylene. A stack of thelayers was joined at the marginal edges of the envelope by squeezing thestack between a pair of points-dies, which were formed with points thatpunctured the kraft paper but not the polyethylene. The points pushedcrowns of un-punctured polyethylene through the punctured holes in thepaper. Then, the marginal edges were squeezed flat between flat-dies,the flat-dies being heated enough to cause fuse-bonding. The margins ofthe finished envelope were held together not only by fuse-bonding, butby the presence of the polyethylene crowns, which, penetrating rightthrough the holes in the paper, serve as mechanical rivets. Thistechnique is termed the pierce-and-fuse technique.

[0071] It is recognised that the pierce-and-fuse technique, as disclosedin the prior patent application in respect of the bubble paddedenvelope, can be utilised in respect of other packaging categories. Inone example, the technique is used to join kraft paper to a planar filmof polyethylene or other thermoplastic material, i.e to ordinary flatplastic film or sheeting, rather than to bubble material. This may beused to produce an envelope, or may be used in respect of objects ingeneral, in which sheets of various materials are joined together.

[0072] In general, the invention may be considered for joining twomaterials where (a) one of the materials has the characteristic that,when pressed by a point, the material is punctured, right through (likekraft, and most kinds of paper); and (b) the other material has thecharacteristic that, when pressed by the same point, the materialstretches beyond its elastic limit, and yields, but is not punctured(like polyethylene and other plastics). The second material should bethermoplastic, i.e when heated, and then cooled, the material loses itsprevious shape and takes on a new shape. With this combination ofcharacteristics, and with some experimentation as to temperatures,squeeze times, etc, satisfactory joints can be made in very many cases.The technique makes use of the application of heat, but the resultingbond is basically a mechanical one. No adhesives or coatings arerequired.

[0073] In place of kraft paper, the technique may be used to joincardboard to polyethylene bubble, or flat film. Cardboard is moredifficult to work with, since its heat capacity is greater than paper,i.e cardboard takes longer to heat up. Cardboard, and many othermaterials, and combinations of materials, need careful control oftemperature. There may be only a few degrees of margin between not hotenough (to fuse and seal the material) and being too hot (which causesburning).

[0074] With some materials, the piercing stage should be done with thepiercing points-dies cold; with other materials, the points-dies may be,or should be, hot. The designer should carry out experiments with theparticular materials, to determine what will be satisfactory in theparticular case.

[0075] When the piercing is done with points-dies that are hot, it maybe possible, with some materials, to combine the thermoplastic fusingstage with the piercing stage, whereby the described subsequent separatehot-squeeze stage may be eliminated. In that case, of course theappearance of the bonded area will be different, in that, if the area ofthe joint is not hot-squeezed flat, the as-finished joint is left withthe form of the indentations caused by the points still present.

[0076] The designer should also experiment with the depth of penetrationof the points. The penetration should be deep enough that the pointsprick right through the paper-like material, and leave the plasticmaterial, not torn, but stretched. The penetration should-be just deepenough that only the tips of the points break through; where the onematerial is fibrous, it is preferred not to break or tear, but ratherjust to separate, the fibres.

[0077] The pierce-and-fuse technique enables sheet polyethylene to bejoined to the very strong, synthetic fibrous smooth-finished material,which is used in some kinds of courier envelope. The material is knownby the (Dupont) trade name Tyvek. Tyvek material can be glued to itself,to form seams, for the purposes of manufacturing the courier envelope.But polyethylene cannot practically be welded or bonded to Tyvek (nor tomany other materials) by the use of glue or adhesive. Only by theaddition of very expensive additives to the adhesives can polyethylenebe glued at all, to most paper-like materials, and the finish of Tyvekmakes it even less amenable. Also, as mentioned, in order to joinpolyethylene to paper or paper-like materials, it is sometimes preferredto pre-laminate a coating of polyethylene right into the paper; butagain, this is hardly practicable with Tyvek.

[0078] But still, it is very desirable to provide an inner bag ofbubble, secured inside a courier envelope of Tyvek, and thepierce-and-fuse technique enables this. The bag made of plastic bubbleliner may be attached only at the marginal edges, and so is separablefor re-cycling. The plastic liner bag may alternatively be done in plainpolyethylene sheet or film.

[0079] As mentioned, the technique can be used to join sheetpolyethylene to sheet cardboard. This is useful in the case ofsubstances (including foodstuffs) that are commonly stored in plasticliner bags inside cardboard boxes. Fixing the plastic bag to thecardboard has been very difficult, using traditional adhesives and liketechniques.

[0080] When gluing food containers, the designer must make sure theadhesives do not release spurious chemical contaminants into the food.Acceptable adhesives for gluing cardboard food boxes, and acceptableadhesives for gluing plastic food bags, are readily available; butinexpensive practical safe acceptable adhesives for gluing polyethyleneto cardboard are not. However, the pierce-and-fuse technique is amechanical, rather than an adhesive, jointing system; the technique doesnot tend to introduce any chemicals that might be toxic in the contextof foodstuffs.

[0081] The technique does not require that materials be pre-coated, andthe technique can be used in cases where the material, for otherfunctional reasons, has a pre-coat of a material that is not compatiblewith practical adhesives. Furthermore, adhesives usually require time tocure or set whereas the present technique the joint bond simply sets asit cools, as in welding.

[0082] The as-illustrated (FIG. 6) pyramid form on the points-dies isadvantageous from the standpoint that the multi-pyramid shapes can bemachined into the die-faces simply by running a suitably profiledgrinding wheel over the die-face. The pyramids thus produced have asharp point, and each pyramid also has four sharp side-edges. The sharppoint penetrates through the paper, but these sharp side-edges do notcut (i.e shear) through the paper; rather, the sharp side-edges may beregarded as creasing the paper and thereby concentrating the squeezingforce, as the dies are brought together, into a narrow line, andpressing the materials together in very intimate contact over thatnarrow line.

[0083] Thus, the pyramid form, in addition to providing the piercedpoints, also provides lines of intimate contact between the twomaterials, around the pierced points. This may be contrasted with, forexample, the needles-style of points-dies, as shown in FIGS. 10,11,which provide only pierced points, but do not provide lines of intimatecontact around the pierced points. The presence of the lines of intimatecontact may be expected to enhance the security of the final fusedjoint.

[0084] The dies as described in the prior disclosure were flat-slabdies. However, it can be inconvenient to provide for the flat-slab diesto advance in the direction in which the materials are being fed throughthe dies. Therefore, the bonding of the joints was done on a stop andstart basis. The materials were fed between the flat-slab dies and thenthe material stops while the dies are in actual operation. On the otherhand, using dies in the form of rollers allows the materials beingbonded to be fed through the rollers on a continuous basis; but it canbe difficult, using rollers, to hold a joint in a squeezed-togetherconfiguration, for longer than a moment.

[0085] Continuous throughput, without stopping and starting, isdesirable, as is holding the joint together for a time period of severalseconds. These conflicting functions can be met if the dies are arrangedto move on tracks, in which the dies are mounted on a flexible carrierhaving a return. Alternatively, the dies can be solid, but mounted on alinkage which allows the die to travel along with the materials; then,upon being withdrawn from the joint area, the die can be returned by thelinkage.

[0086] As mentioned, the points should be arranged to penetrate rightthrough the paper—and, when the items being joined are sandwichedbetween two sheets of paper, through both sheets of paper—to the extentthat pinpoints of light would be visible if the joint area were to beheld up to the light. In fact, these pinpoints of light can serve as thebasis for an inspection technique. To do this, the pierced area ispassed under a light source, and a sensor determines the extent to whichlight shines through. If the pinpoints are too small, or too large, oruneven, the machine can be stopped, and adjustments made. Or, theadjustments can be done automatically, responsively to the sensorsignals. Often, the only adjustment required is in respect of thedistance apart of the dies as they close together, or bottom out, andthe extent to which the dies squeeze the sandwich is readily adjusted bythe insertion of appropriate die-closure shims.

[0087] As shown in FIGS. 12a,12 b, the upper and lower points-dies havebeen brought together until the points just touch a stack 60 of sheets.Insofar as the sheets include bubble material, the bubbles arecollapsed, in the drawings, whereby the thickness H of the stack is theaggregate of the thicknesses of the material itself of each sheet. Thepoints-dies now lie a reference-distance S mm apart. In FIG. 12b, thepoints-dies have been closed together, whereby now thematerial-thickness of the stack 60 is compressed between the dies, andof course, the sheets that make up the stack have been stretched overthe points. The points-dies now lie a distance C apart. Thus the dieshave moved together a distance S−C=M. The designer should arrange thedimensions of the points such that the distance M is about one mm.

[0088] The type of kraft paper used for bubble envelopes typically is0.1 mm thick, and the polyethylene film from which the bubble is madetypically is about 0.05 mm thick. It has been found that, with a stackof two sheets of kraft paper, and two sheets of bubble film, when thedistance M is about one mm, the points just break right through thepaper, and also cause the polyethylene of the bubble film to bestretched almost ideally in the manner as shown in FIG. 8. The plasticfilm is stretched beyond its elastic limit, and takes a permanent set,as the crowns are pushed through the holes punctured in the paper. Ifthe distance M were more than about two mm, too much of the paper wouldbe torn, which might weaken the envelope; if M were less than about ahalf-mm, the points would not break through the paper reliably.

[0089] If the points were to be pushed too far through the paper, thepaper might be weakened. Each of the punctured points in the paperpreferably should be surrounded by a bridge of intact paper, forming acontinuous ring around the point. (This does not apply to the points atthe very edge of the paper, of course.) The continuous ring around eachpoint should be nowhere less than one mm wide.

[0090]FIG. 13 is a plan view of a grid of points, where the grid spacingbetween adjacent points, as produced by one of the points-dies, is P mm.The points produced by upper points-die (the up-points) are shown asdots, whereas the points produced by the lower points-die (thedown-points) are shown as crosses. The up-points protrude downwards intothe paper, whereas the down-points protrude upwards out of the paper. Itwill be understood that the point-to-point spacing of the grid ofpoints, as a whole, now is P1. Assuming the dies (i.e the points) areaccurately identical, orthogonal, and symmetrical, the distance P1 isP.½{square root}{square root over ( )}2 mm.

1. Procedure for attaching a sheet of puncturable-material to a sheet ofstretchable-material, including: wherein the puncturable material ismaterial that, upon being forcefully stretched over a point, is readilythrough-punctured, substantially without stretching; wherein thestretchable material is material that, upon being forcefully stretchedover a point, readily stretches over the point, substantially withoutbeing through-punctured by the point; making a stack of sheets ofpuncturable material and stretchable material, in which the sheets liein direct face-to-face touching contact with each other; providing apoints-die; wherein a points-area of the points-die has many protrudingpoints, which point towards the stack; wherein the points-area liesover, and thereby defines, an adherence-area of the stack; pressing andsqueezing the points-die onto the adherence-area of the stack; thenseparating the stack from the points-die.
 2. Procedure of claim 1,wherein the configuration of the points, and the manner of squeezing thepoints-die onto the stack, is such that, when the stack is squeezed bythe points-die: substantially all of the points break through, and makeholes right through, the puncturable material; and substantially none ofthe points breaks through, and makes holes right through, thestretchable material.
 3. Procedure of claim 2, wherein the configurationof the points, and the manner of squeezing the points-die onto thestack, is such that, when the stack is squeezed by the points-die,crowns of the stretchable material become stretched over the points farenough for the stretchable material to be stretched beyond its elasticlimit, and to take a permanent set.
 4. Procedure of claim 1, wherein thepuncturable material is characterised as a paper material, for examplekraft paper.
 5. Procedure of claim 1, wherein the puncturable materialis a light, strong, tear-resistant, synthetic-fibrous, smooth,paper-like material, for example Tyvek (TM).
 6. Procedure of claim 1,wherein the stretchable material is characterised as a plastic filmmaterial, for example polyethylene film.
 7. Procedure of claim 1,wherein the stretchable material is bubble material, in which a baselayer of plastic film material is adhered over part of its surface areato a bubble layer of plastic film material, leaving bubblestherebetween.
 8. Procedure of claim 1, wherein the stack is comprised ofthe following sheets of the materials: puncturable; stretchable;stretchable; puncturable.
 9. Procedure of claims 4 and 7, wherein thestack is comprised of the following sheets of the materials: paper;bubble; bubble; paper.
 10. Procedure of claim 1, wherein the puncturablematerial is a metal foil material, for example aluminum foil. 11.Procedure of claim 1, including pressing the points-die hard enough topuncture the puncturable-material immediately over the points, butlightly enough to leave a bridge of the puncturable material stillintact, between the points.
 12. Procedure of claim 11, including:wherein some of the points are edge-points, being those points inrespect of which no other one of the points lies nearer to an edge ofthe stack; pressing the points-die onto the stack in such manner that,upon the stack being separated from the points-die, in respect of eachof the points that is not an edge-point, there remains a bridge ofintact material between adjacent points; and the bridge forms acontinuous ring around each one of the points.
 13. Procedure of claim12, wherein, in respect of each point, the continuous ring is nowhereless than 1 mm wide.
 14. Procedure of claim 1, including providing anupper points-die and a lower points-die, wherein: the upper and lowerpoints-dies have respective points-areas, which are co-extensive withthe adherence-area of the stack; the points-area of the upper points-diehas many protruding points, being the upper points, which are pitched ona grid a distance P mm apart; the points-area of the lower points-diehas many protruding points, being the lower points, which are alsopitched on a grid the said distance P mm apart; the upper points lie ina staggered relationship with respect to the lower points; the upperpoints fit into the spaces between the lower points when the points-diesare brought together; upon the points-dies being pressed and squeezedonto the adherence-area, up-points on the adherence-area produced by theupper points lie intercalated with down-points on the adherence-areaproduced by the lower points; whereby the up-points and the down-points,on the adherence-area of the stack, together lie pitched on a grid adistance P.½{square root}{square root over ( )}2 mm apart.
 15. Procedureof claim 14, wherein the configuration of the points-dies is such that:—the points-dies have a slack-take-up separation, being S mm, being theseparation of the points-surfaces at which a flat layer of materialhaving a thickness of H mm lies between, and just touching, the upperand lower points-surfaces, without the material of the layer beingstretched over the points; the points-dies have a closed-togetherseparation, being C mm, being the separation of the points-surfaces atwhich the dies lie closed together onto the flat layer of thickness Hmm; and the distance the points-dies move together, in going from aseparation of S mm to a separation of C mm, being S−C, is M mm; and M mmis between ½ mm and 2 mm, and preferably is about 1 mm.
 16. Procedure ofclaim 14, wherein the points are pitched a distance P apart, P being theclosest distance between adjacent points, where. P is between 1½ mm and5 mm, and preferably is about 3 mm.
 17. Procedure of claim 14, whereinthe points are provided on the points-surface of the points-die aspointed pyramids.
 18. Procedure of claim 17, wherein the pyramids areregularly-pitched, on a grid in which the pyramids are pitched adistance P apart, where P is between 1½ mm and 5 mm, and preferably isabout 3 mm.
 19. Procedure of claim 14, including the following procedurefor manufacturing the points-dies: passing a cutting wheel, having aV-shaped cutting profile, in such manner as to form V-shaped grooves,over the points-die in a first direction, and passing a cutting wheel,having a V-shaped cutting profile, over the die in a second direction;wherein the second direction is orthogonal to the first direction; andmaking the grooves deep enough that pointed pyramids are left betweenthe grooves.
 20. Procedure of claim 19, wherein the V-shaped profile hasan included angle of between 90 degrees and 60 degrees.
 21. Procedure ofclaim 14, wherein: after the points-dies have been pressed and squeezedonto the adherence-area, the puncturable material remains intact, andnot punctured, over a bridge portion of the puncturable material,between the up-points and the down-points; and the un-punctured bridgeportion is at least 1 mm wide.
 22. Procedure of claim 1, including:providing a flattening-die; after separating the stack from thepoints-die, placing the flattening-die against the adherence-area of thestack; squeezing the adherence-area of the stack with theflattening-die, in such manner as to flatten the adherence-area. 23.Procedure of claim 22, including: providing the stretchable-material asa thermoplastic material, having a thermoplastic temperature threshold;heating the material above the said threshold; while the materialremains above the said threshold, squeezing the adherence-area of thestack with the flattening-die; then separating the stack from theflattening-die, and allowing the material to cool.
 24. Procedure ofclaim 8, wherein: the sheets of material are arranged in the stack so asto form the front and back of an envelope, having left and right edgesand a bottom edge, which are closed, and having a top edge, which isopen, and which includes a fastener for closing the envelope; theadherence-area is a relatively-narrow continuous marginal area,contiguous with the left, right, and bottom edges; the procedure iscarried out in such manner as to ensure that, over at least a majorproportion of the total area of the stack of sheets, the sheets are notadhered together.
 25. Procedure that falls within the scope of claims 2,9, 17, 20, 21, and 23, wherein: the sheets of material are arranged inthe stack so as to form the front and back of a bubble envelope, havingleft and right edges and a bottom edge, which are closed, and having atop edge, which is open, and which includes a fastener for closing theenvelope; the adherence-area is a relatively-narrow continuous marginalarea, contiguous with the left, right, and bottom edges; the procedureis carried out in such manner as to ensure that, over at least a majorproportion of the total area of the stack of sheets, the sheets are notadhered together.
 26. An envelope that has been manufactured by aprocedure that falls within the scope of claim
 24. 27. A padded bubbleenvelope that has been manufactured by a procedure that falls within thescope of claim 25, in which the adherence-area is free of glue oradhesive.
 28. A production machine, being so structured and arranged asto be suitable for carrying out a procedure that falls within the scopeof claim 25, to produce envelopes that fall within the scope of claim27.